1. Technical Field
The present invention relates generally to evaporative emission control systems for automotive vehicles and, more particularly, to a method of compensating for purge vapors from an evaporative emission control system for an automotive vehicle.
2. Discussion
Modem automotive vehicles typically include a fuel tank and an evaporative emission control system that collects volatile fuel vapors generated in the fuel tank. The evaporative emission control system includes a vapor collection canister, usually containing an activated charcoal mixture, to collect and store volatile fuel vapors. Normally, the canister collects volatile fuel vapors which accumulate during refueling of the automotive vehicle or from evaporation of the fuel. The evaporative emission control system also includes a purge valve placed between an intake manifold of an engine of the automotive vehicle and the canister. At certain times conducive to purging, the purge valve is opened by an engine control unit an amount determined by the engine control unit to purge the canister, i.e., the collected volatile fuel vapors are drawn into the intake manifold from the canister for ultimate combustion within a combustion chamber of the engine.
As one skilled in the art will appreciate, the entry of purge vapors into the combustion chambers of the engine change the combustion characteristics of the engine. More particularly, the presence of purge vapors in the intake manifold change the required amount of fuel injected from the fuel injectors to maintain optimum drivability. Injecting too much fuel in the presence of the purge vapors causes an improper fuel to air ratio which may result in incomplete combustion, rough engine operation and poor emissions.
Although prior art methods of accounting for purged volatile fuel vapors from the evaporative emission control system have achieved favorable results, there is room for improvement in the art. For instance, it would be desirable to provide a method of identifying the source of the vapors from within the evaporative emission control system based on source characteristics, anticipating variations in the level of purge vapors using learned information from the identified source, and adjusting the amount of fuel delivered from the fuel injectors in accordance with the variations and sources of the purge vapors to maintain a desired fuel to air ratio.